The present disclosure is generally directed to toner processes, and more specifically to processes comprising aggregating and coalescing toner particles from an aqueous suspension of colorant, wax particles and resin particles. In embodiments, described is the preparation of an ultra low melt polyester toner comprised of colorant, wax, an amorphous resin and a crystalline resin. Ultra low melt particles typically display a melting point of from about 50° C. to about 100° C.
EA techniques typically involve the formation of a latex emulsion of the resin particles, which particles have a size of from about 5 to about 500 nanometers in diameter. The resin may be heated, optionally with solvent if needed, in water, or by making a latex in water using emulsion polymerization. A colorant dispersion, for example of a pigment dispersed in water, optionally also with additional resin, may be separately formed. The colorant dispersion may be added to the emulsion latex mixture and an aggregating agent or complexing agent may then be added to initiate aggregation of larger size toner particles. Once a desired toner particle size is achieved, aggregation may be stopped. The aggregated toner particles may then be heated to enable coalescing/fusing, thereby achieving aggregated, fused toner particles.
Fundamental to the performance of a toner is its ability to maintain charge requirements. The ambient environment, which has been classified into three zones, can affect this ability. The A-zone is characterized by high humidity and high temperature (about 28° C. and about 85% relative humidity). The B-zone is characterized by moderate humidity and temperature (about 21° C. and about 40% relative humidity). The C-zone is characterized by low temperature and low humidity (about 10° C. and about 40% relative humidity). If there is a large difference in charging behavior across these zones, the materials have a sensitivity to relative humidity. The sensitivity ratio may be expressed as a ratio of a triboelectric charge of the toner developer in the C-zone to a triboelectric charge of the toner developer in the A-zone. A goal is for the RH sensitivity ratio to be as close to one as possible.
Polyester based toners may display low charge due to polyester's hydrophilic nature as compared to other toners. With additives, the polyester resins can meet the charge requirements of a toner.
An advantage to using polyester-based toners is the ability to produce low melting toner, for example ultra-low melt toner, via inclusion of crystalline polyester in the toner. However, when a crystalline component is added to these resins to lower the melting point of the toner, the present inventors have found that the high resistivity of the crystalline polyester may contribute to lower charge and lower charge maintainability as well as higher cohesion if coalesced at temperatures above the onset of melt point of the crystalline resin, wherein plasticization of the resin occurs.
Following discovery of these issues, the inventors sought a solution to these potential problems associated with the use of crystalline polyester.